Schizochlamydella orbicularis Novis & Visnovsky, 2012

Novis, Phil M. & Visnovsky, Gabriel, 2012, Novel alpine algae from New Zealand: Chlorophyta, Phytotaxa 39, pp. 1-30 : 20-22

Schizochlamydella orbicularis Novis & Visnovsky , sp. nov. ( Figs 4D–E )

Cellulae sphaericae vel subsphaericae, 3.1–6.1 µm latae. Paries cellularis tenuis laevisque. Chloroplastus viridis , parietalis, lobatus, in cellulis valentibus incisuris 2–4 instructus. Pyrenoides nulla. Cellulae coloniales, mucilaginae maturae per matricem mucilaginis achromaticam instratosam uniformiter aequidistantes. Autosporis 2–4–8 per sporangium regenerans, eae per expansionem matricis gradatim separantes.

Type:— NEW ZEALAND: Westland : Mt Philistine, 1400 m, preserved cultured specimen from sample collected 30 November 2007, CHR610488 .

Cells colonial, spherical or near-spherical, 3.1–6.1 µm wide. Cell wall thin and smooth. Chloroplast green, parietal, lobed, with 2–4 incisions in healthy cells. Pyrenoid absent ( Fig. 4E ). Colonies mucilaginous, mature cells spaced evenly through colourless, unlayered mucilage matrix ( Fig. 4A ). Reproduction by autospores, 2–4–8 per sporangium, gradually separating through expansion of mucilage matrix ( Fig. 4A ). Sequence data for both the rbc L and 18S rDNA genes suggested that the species formed a novel lineage in the Trebouxiophyceae, with no clear affinities ( Figs 8 , 9 ).

Habitat:— Alpine herbfield soil.

Distribution:— New Zealand.

Etymology:— “Spherical shaped”, referring to the cell.

Observations:— The morphology of this species—mucilaginous colonies, lack of pyrenoids and zoospores—suggests an affinity with Coccomyxa , yet S. orbicularis is clearly a distant relative of species in the Coccomyxa clades. More discussion of these clades is given in remarks on Pseudococcomyxa simplex (below). The colonial mucilaginous habit lacking zoospores accords with the Radiococcaceae sensu Ettl & Gärtner (1995) . Of the genera therein, the New Zealand strain most closely matches Schizochlamydella Korshikov (1953) , with cells irregularly dispersed in homogeneous mucilage. Only one other species of Schizochlamydella lacks a pyrenoid, namely S. minutissima Broady (1982) . However, this species is slightly smaller than our strain, with ellipsoidal juvenile cells. One species has previously received attention at the molecular level ( Wolf et al. 2003): Schizochlamydella capsulata ( Watanabe 1977) . This strain is distinguished from our material by containing one or more pyrenoids, and is placed in the Oocystaceae using 18S rDNA sequences ( Wolf et al. 2003), not closely related to S. orbicularis ( Fig. 8 ). Given the paucity of characters available to classify these species, it is not surprising that morphology does not reflect phylogeny. Typification in the genus Schizochlamydella is problematic, however. The type species of the genus, S. delicatula (West) Korshikov (1953) was transferred to the chrysophycean genus Phaeoschizochlamys Lemmerman (1898) by Bourrelly (1957). However, this transfer was made without pigment or molecular analyses; we regard the choice of Schizochlamys for our material as prudent until the phylogenetic placement of the type species is clearly established.

Cultures:— LCR-CG9.

Figures

FIGURE 4. A–C. Achoma brachiatum (photographed from culture LCR-CG11). A. Light micrograph of vegetative cells showing variable shape, prominent pyrenoid (pyr), and incised parietal chloroplast (cp). B, C, Transmission electron micrographs of zoospore showing mitochondria (mito), chloroplast containing starch (st) and prominent pyrenoid (pyr), components of flagellar basal apparatus (fba), absence of cell wall, and branching pattern of thylakoids (tm) in the pyrenoid matrix. D, E Schizochlamydella orbicularis (photographed from culture LCR-CG9). D. Light micrograph of mature cells evenly spaced in mucilage, and newly released autospores (arrow). E. Transmission electron micrograph of cell showing mitochondrion (mito), nucleus (nuc) cell wall (cw), and parietal chloroplast containing starch (st) but no pyrenoid. Scales: 10 µm in D (use for A and D), 1 µm in B, C, and E.

FIGURE 8. Phylogenetic analysis of the Trebouxiophyceae inferred from 18S rDNA sequences. Sequences contributed in this study are in bold. The tree typology is that inferred using MrBayes v3.0B4 (5 million generations). Numbers associated with nodes are Bayesian PP/MPB percentages (500 replicates). Scale bar represents 0.1 changes/site.

FIGURE 9. Phylogenetic analysis of a combined dataset representing the Chlorophyceae and Trebouxiophyceae inferred from rbcL gene sequences, with the third codon position omitted. Sequences contributed in this study are in bold. The tree typology is that inferred using MrBayes v3.0B4 (5 million generations). Numbers associated with nodes are Bayesian PP/MPB percentages (500 replicates). Scale bar represents 0.1 changes/site.